1. Field of the Invention
The present invention relates to an input device that is incorporated in an electronic instrument. More specifically, the invention relates to an input device that detects at least one of the pressing direction and the pressing force based on a change in capacitance when an arbitrary position of the input device has been pressed.
2. Description of Related Art
A capacitance force sensor that allows a two-axis or three-axis input operation has been known as an input device that is incorporated in an electronic instrument (see JP-A-2005-38623, for example).
Such a sensor includes a printed circuit board that includes a base (e.g., glass epoxy) and provided with fixed electrodes, a movable electrode that is formed of a conductive rubber and spaced apart from the fixed electrodes to be opposite to the fixed electrodes, and a metal or resin casing that secures the printed circuit board and the movable electrode.
The fixed electrodes include four fan-shaped electrodes that are disposed concentrically with respect to the center of the sensor. Two electrodes disposed along the X-axis are, used as direction Y input detection electrodes, and two electrodes disposed along the Y axis are used as direction Y input detection electrodes. A Z-axis direction input detection electrode is disposed on the inner circumferential side or the outer circumferential side of the four electrodes.
A change in capacitance that occurs when an arbitrary position of the movable electrode has been pressed can be detected using these electrodes.
However, since many parts are required to form the capacitance force sensor, the cost of the capacitance force sensor increases.
It is difficult to reduce the total thickness of the capacitance force sensor since a reduction in thickness of each part (material) is limited. This makes it difficult to incorporate the capacitance force sensor in a thin electronic instrument.
Moreover, the capacitance force sensor has a large two-dimensional area, and may interfere with other parts (e.g., switch). Therefore, the capacitance force sensor has not been widely incorporated in an electronic instrument.
An input device that includes a plurality of fan-shaped electrodes that are disposed concentrically, and detects a change in capacitance that occurs when the electrodes are traced with a finger or the like. (see JP-T-2007-503052, for example).
This device can detect whether the user has traced the detection section clockwise or counterclockwise when the user has circularly traced the detection section with a finger, and has been applied to a volume operation or a scroll operation of a portable audio instrument.
The above input device can detect a simple two-dimensional input operation (e.g., scroll operation), but cannot detect the pressing force due to the detection principle.